1. Field of the Invention
The present invention generally relates to providing redundancy for volatile memory. More particularly, the invention relates to applying “RAID” techniques to a plurality of replaceable processing units having integrated volatile memory.
2. Background of the Invention
As is commonly known, a computer typically includes at least one central processing unit (“CPU”), random access memory, mass storage, input/output devices and numerous other components. Such components are coupled together through one or more digital connections called “busses.”
To improve system performance, one trend has seen the integration of memory controllers, memory and a CPU on a “processing” module. Such modules typically have a connector which enables the module to be plugged into a computer system's main system board. Such computer systems, in fact, may be able to accommodate multiple processing modules. In a system with multiple processing modules, the CPU of one module can access its own memory or the memory of another module. This type of architecture permits computer systems to be scalable so as to increase the number of CPUs and memory.
Another trend in the computer arts has been to make various components “hot pluggable.” A hot pluggable component is one that can be installed into a system that is already powered up and running. This type of component installation is in contrast to non-hot pluggable components which can only be installed into a system that is first powered off, and then powered on after the component has been installed. Typically, hot pluggable components can also be hot removable meaning they can be removed from a system without first powering off the system. Such hot pluggable-based systems include a mechanism to detect when a component has been removed or installed.
The trend towards hot pluggable components has created a desire to be able to hot remove and install processing modules as described above. However, because such modules include RAM memory which is volatile, meaning that the contents of the memory are lost once power is turned off to the memory device, a decision must be made by the system designer as to what should happen to the data that is stored on a processing module when it is removed and replaced. When the processing module is removed, power is lost to the module of course and the data contained on the volatile memory in the module effectively is erased. One approach might be simply to live without the data and the degradation that may be caused by the loss of the data. This approach may be simple to implement, but the loss of data may not be desirable in many applications, particularly for mission critical applications.
Accordingly, it would be desirable to be able to retain the data on a processing module that is removed from a computer system so that, upon replacement with a new module, the new module can be loaded with the data from the old module. Despite the advantages such a system would provide, to date no such system is known to exist.